1. Field of the Invention
The present invention relates generally to an x-ray film holder and associated alignment rod which rotate together relative to a stationary biteblock for use in dental radiography. By the nature of the configuration herein described, the invention is especially useful for, but not limited to, film holder biteblock arrangements which are laterally off-set one to the other when viewed from the x-ray source. Such lateral off-set instruments are useful for endodontic radiography.
2. Description of the Related Art and Summary of the Invention
When taking dental periapical radiographs, because of the curvature of the palate and the various angulations of the roots of the teeth, as well as observance of the rules of the paralleling and bisecting angle techniques, it is often necessary to place the film in the mouth at an angle between 90 and 180 degrees with respect to the occlusal plane. When the film holder and beam alignment rod are rigidly fixed to the biteblock, which is the case with much of the prior art e.g. U.S. Pat. No. 3,473,026, it is necessary to angle the biteblock with respect to the occlusal surfaces of the teeth in order to achieve the desired angle of the film holder. When the biteblock is at an angle i.e. not parallel to the biting surfaces of the teeth, it cannot be grasped with maximum security between the upper and lower teeth, and, at times, it cannot be grasped at all. This results in the operator having to compromise by changing the angle of the film holder to a less than optimal one.
With respect to prior art, patented device, U.S. Pat. No. 4,866,750, although providing a rotatable film holder, does not present a means of keeping the spatial relationship between the film holder and x-ray source constant. Specifically, the film holder rotates with respect to the x-ray source i.e. the angle between the cross-sectional plane of the x-ray beam and the film holder changes with rotation of the film holder. It is imperative in dental radiography, when employing the "parallel technique", that the cross-sectional plane of the x-ray beam and the plane of the surface of the film to be irradiated are parallel. This parallelism minimizes distortion of the resultant radiographic image.
U.S. Pat. No. 4,538,292 describes a biteblock which rotates or deflects about an axle. It is this rotation, or deflection, which causes the biteblock to be more securely grasped between the upper and lower teeth. The film holder and alignment rod cannot be rotated to an angle selected by the operator.
The herein disclosed invention offers distinct advantages with respect to the prior art. By securing a rotatable axle to, or within, the biteblock, and attaching the film holder to one end of an extension bar, and attaching the other end of the extension bar to the rotatable axle, and further attaching a beam alignment rod to the other end of the axle, the film holder and alignment rod can rotate, while the biteblock remains stationary. Further, the biteblock and alignment rod can rotate together, and, consequently, the predetermined spatial relationship of the film to the x-ray beam remains constant for all angles of the above mentioned rotation. And this rotation is possible while the biteblock is maximally secured between the upper and lower jaws in a position parallel to the occlusal plane. For example, when using the paralleling technique for dental radiography, the angular relationship of the cross-sectional plane of the x-ray beam with the surface of the film should be 0 degrees, i.e. parallel. This parallelism will be maintained for all angles of rotation of the axle in the aforementioned device while the patient is biting on a biteblock securely held parallel to the occlusal plane.
Patented device, U.S. Pat. No. 4,633,493, offers a rotatable biteblock while maintaining a constant spatial relationship between film holder and x-ray source. However, it uses two wing-like biteblocks secured to the two ends of a transverse axle. The film holder and x-ray alignment rod are attached to the center of the axle, in contrast to being attached to opposite ends of an axle as described previously. This center attachment design precludes its use with x-ray positioners which have the biteblock laterally offset to the film holder when viewed from the x-ray source. The lateral offset makes it possible for these instruments to be used during endodontic treatment. Endodontic files and rubber dam clamp are unaffected by the biteblock. The herein disclosed invention has an advantage by offering a means for the film holder, when laterally off-set to the biteblock when viewed from the x-ray source, to rotate together with the alignment rod.
By offering a means of rotation for the above described laterally off-set film holder devices e.g. U.S. Pat. No. 4,598,416, another problem is alleviated by the herein disclosed invention. With the laterally off-set film holder instruments, it is often necessary, when taking a posterior radiograph, for example, to place the biteblock between the anterior teeth. In this position the biteblock cannot be placed at an angle in the latero-medial direction of the curvature of the palate because the anterior teeth cannot serve as a fulcrum. However, by securing a rotatable axle to or within the biteblock, and attaching the film holder and the beam alignment rod in the manner previously described for the herein disclosed invention, the film holder can be rotated to the desired angle, while the biteblock remains stationary between the upper and lower anterior teeth. Consequently, the spatial relationship e.g. parallel, between the film and the cross-sectional plane of the x-ray beam (via the beam alignment rod with positioning ring) remains constant with all angles of rotation of the axle.
Although the drawings herein depict the device having a configuration consistent with taking radiographs of posterior teeth, it should not be assumed that this invention is limited to being used in the posterior area. This device works equally well for taking radiographs in the anterior region of the mouth and of the anterior teeth.
Accordingly, it is first an object of this invention to provide an x-ray film positioner for intra-oral radiography that can be held in a maximally secured fashion between the upper and lower teeth, while the film holder, and the therein contained film, can be optimally angulated with respect to the structures to be radiographed.
Further, it is an object of this invention to provide a means by which the predetermined angle, or spatial relationship e.g parallel, between the film and x-ray source will be maintained for all angles of rotation of the film holder with respect to the oral structures and teeth.
It is an additional object of this invention to provide a means by which x-ray film positioners for intra-oral radiography, which have their film holders laterally off-set to their biteblocks when viewed from the x-ray source, can be securely held by the anterior teeth when taking a radiograph of the posterior teeth, regardless of the angulation of the film holder and beam alignment rod.